ST10F271 datasheet(37/173 Pages) STMICROELECTRONICS

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ST10F271

Internal Flash memory

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5.5.6

XBus flash volatile temporary access unprotection register (XFVTAUR0)

5.5.7

Access protection

The I-Flash module has one level of access protection (access to data both in Reading and

Writing): if bit ACCP of FNVAPR0 is programmed at 0 and bit TAUB in XFVTAUR0 is set at

0, the I-Flash module becomes access protected: data in the I-Flash module can be read

only if the current execution is from the I-Flash module itself.

To enable Access Protection, the following sequence of operations is recommended:

●

execution from external memory or internal Rams

●

program TAUB bit at 1 in XFVTAUR0 register

●

program ACCP bit in FNVAPR0 to 0 using Set Protection operation

●

program TAUB bit at 0 in XFVTAUR0 register

●

Access Protection is active when both ACCP bit and TAUB bit are set to 0.

Protection can be permanently disabled by programming bit PDS0 of FNVAPR1H, in order

to analyze rejects. Protection can be permanently enabled again by programming bit PEN0

of FNVAPR1L. The action to disable and enable again Access Protections in a permanent

way can be executed a maximum of 16 times. To execute the above described operations,

the Flash has to be temporary unprotected (See Section 5.5.9: Temporary unprotection)

Trying to write into the access protected Flash from internal RAM or external memories will

be unsuccessful. Trying to read into the access protected Flash from internal RAM or

external memories will output a dummy data (software trap 0x009Bh).

When the Flash module is protected in access, also the data access through PEC of a

peripheral is forbidden. To read/write data in PEC mode from/to a protected Bank, first it is

necessary to temporary unprotect the Flash module.

In the following table a summary of all levels of possible Access protection is reported: in

particular, supposing to enable all possible access protections, when fetching from a

memory as listed in the first column, what is possible and what is not possible to do (see

column headers) is shown in the table.

XFVTAUR0 (0x00 EB50)

NVR

Reset value: 0000h

987

65432

TAUB

reserved

Table 23.

XBus flash volatile temporary access unprotection register

Bit

Function

TAUB

Temporary Access Unprotection bit

If this bit is set to 1, the Access Protection is temporary disabled.

This bit can be written only executing from IFlash.This fact guarantees that only a

code executed in IFlash, can unprotect the IFlash, when it is Access Protected.

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